This invention relates to a process for the manufacture of glycerine from mixtures of chlorohydrins. More particularly, this invention is directed to an improved process for alkali metal carbonate catalyzed hydrolysis of chlorohydrin mixtures containing epichlorohydrin and mono and dichlorohydrins wherein a two phase, liquid solvent system is employed in combination with low reaction temperatures to maximize the selectivity with which the mixed chlorohydrin feedstock is converted to glycerine.
It is well known that glycerine can be synthesized by aqueous phase hydrolysis of chlorohydrins with alkali metal carbonate catalysts, e.g., see U.S. Pat. Nos. 2,318,032, 2,810,768 and 2,838,574. While earliest disclosures on this synthetic technique, i.e., U.S. Pat. No. 2,318,032 indicate that the reaction can be carried out over a rather broad temperature range, i.e., 50.degree. to 250.degree. C. with a broad variety of chlorohydrin reactants, the thrust of more recent prior art teachings has been in the direction of high reaction temperatures and chlorohydrin reactants made up predominantly, if not exclusively, of epichlorohydrin. In this regard both U.S. Pat. Nos. 2,810,768 and 2,838,574 teach the use of reaction temperatures above 75.degree. C. and prefer or specify reaction temperatures which are sufficiently high-- i.e., 100.degree. to 200.degree. C. in U.S. Pat. No. 2,838,574 and 130.degree. to 200.degree. C in U.S. Pat. No. 2,810,768-- to require the use of a pressurized reaction system. Further, at least U.S. Pat. No. 2,810,768 is limited on its face to the use of a chlorohydrin reactant feedstock made up substantially, if not exclusively, of 1-chloro-2,3-epoxypropane or epichlorohydrin.
The primary benefits of this high reaction temperature hydrolysis are short contact or residence times coupled with a purported high selectivity in the conversion of chlorohydrin reactants to glycerine. However, in practice this high selectivity to glycerine is apparently limited to the use of reactant streams made up substantially of epichlorohydrin in contrast to the glycerol chlorohydrins such as the isomeric dichlorohydrins and monochlorohydrins obtained by conventional chlorohydrination of allyl chloride. In fact, the accepted commercial technique for the conversion of allyl chloride to glycerine typically involves a caustic hydrolysis step after chlorohydrination wherein the glycerol dichlorohydrins are substantially converted to epichlorohydrin with the resultant epichlorohydrin being subject to high temperature carbonate catalyzed hydrolysis to afford glycerine. In this process, the presence of significant amounts of unreacted glycerol chlorohydrins in the epichlorohydrin feed stream to high temperature hydrolysis apparently leads to unwanted side reactions forming heavy ends and difficult to remove by-products which boil near glycerine. While the amount of glycerol chlorohydrins in the epichlorohydrin feed to high temperature hydrolysis can be reduced by recycle of unreacted glycerol chlorohydrins to the chlorohydrin hydrolysis reaction, conventional operation of the process invariably affords one or more waste streams containing glycerol chlorohydrins which must be passed to waste or effluent disposal to avoid the formation of undesirable by-products. These waste streams represent a loss in the overall yield of glycerine from allyl chloride in the process as well as an additional burden on waste treatment facilities.
From the foregoing it is apparent that considerable advantage would be obtained if a chlorohydrin hydrolysis process could be developed in which the full range of possible chlorohydrin reactants including glycerol mono- and dichlorohydrins in addition to epichlorohydrin could be selectively converted to glycerine with a minimum of by-product formation.